Radiation Dose to the Breast by 64-slice CT: Effects of Scanner Model and Study Protocol.

RATIONALE AND OBJECTIVES: This work aimed to study the effects of scanner model and study protocol on radiation dose received by breast tissues from 64-slice computed tomography (CT) studies. MATERIALS AND METHODS: Four scanner models and three study protocols were used in scanning an anthropomorphic phantom with breast modules. Each protocol follows recommendations or guidelines from the American Association of Physicists in Medicine and the American College of Radiology. Twenty thermoluminescent dosimeters were placed inside the breast modules to measure breast tissue doses. Both the absolute and the normalized breast tissue doses were analyzed. RESULTS: The mean glandular doses of a lung cancer screening CT, a chest/abdomen/pelvis CT, and a virtual colonoscopy CT are equivalent to less than 1, 5-7, and 1-3 two-view digital mammograms, respectively, for a standard-sized patient. The normalized breast dose differs significantly (P < 0.01) between lung cancer screening CT and chest/abdomen/pelvis CT; however, it shows less than ±10% variation among scanner models for the same protocol. In virtual colonoscopy CT, breast tissue dose decreases with the distance between local tissues to the edge of the x-ray field, although the decreasing trend varies for different scanner models and protocol settings. CONCLUSIONS: When breasts are entirely included in the primary x-ray field, breast dose by 64-slice CT is mainly protocol dependent, with the normalized breast dose about 15% lower for protocols with modulated mA than for those with constant mA; when breasts are only partially included in the primary beam field, breast dose by 64-slice CT is dependent on both the scanner model and the protocol settings.

Atypical brain torque in boys with developmental stuttering.

The counterclockwise brain torque, defined as a larger right prefrontal and left parietal-occipital lobe, is a consistent brain asymmetry. Reduced or reversed lobar asymmetries are markers of atypical cerebral laterality and have been found in adults who stutter. It was hypothesized that atypical brain torque would be more common in children who stutter. Magnetic resonance imaging-based morphology measures were completed in boys who stutter (n = 14) and controls (n = 14), ages 8-13. The controls had the expected brain torque configurations whereas the boys who stutter were atypical. These results support the hypothesis that developmental stuttering is associated with atypical prefrontal and parietal-occipital lobe asymmetries.

Relevance of subcortical stroke in dysphagia.

BACKGROUND AND PURPOSE: Unilateral cortical lesions are associated with dysphagia in ischemic stroke. It is unclear, however, whether acute subcortical stroke is associated with a similar risk of dysphagia. The aim of this study was to determine the occurrence of dysphagia in purely subcortical stroke and identify dysphagia characteristics. METHODS: Between 2003 and 2005, videofluoroscopic swallow studies (VFSSs) were completed in 20 consecutive ischemic stroke patients with purely subcortical lesions (right hemisphere damage [RHD]=10, left hemisphere damage [LHD]=10) and 25 age-matched controls. Individuals were classified with dysphagia when at least 2 swallowing measures were 2 standard deviations above mean scores for the control group. Lesion volume, hemisphere, and location were determined from diffusion-weighted magnetic resonance imaging scans. RESULTS: Seven subcortical stroke patients (35%) met VFSS criteria for dysphagia (LHD=5, RHD=2); 4 patients presented with clinically significant dysphagia. A significant interaction between hemisphere and lesion location was identified. Whereas 3 of 5 patients with dysphagia (60%) had lesions to the left periventricular white matter (PVWM), LHD patients without dysphagia did not have PVWM lesions. In contrast, no RHD patients with PVWM lesions had dysphagia, and 6 of 8 patients without dysphagia (75%) had PVWM lesions. Oral transfer was significantly slower in patients with subcortical stroke compared with the healthy adults. CONCLUSIONS: Lesions to the left PVWM may be more disruptive to swallowing behavior than similar lesions to the right PVWM. Swallowing deficits involving oral control and transfer may be a marker of subcortical neural axis involvement.

fMRI characterization of the language formulation area.

Participants read sentences presented one word at a time, half of which ended with a semantically incongruent ending. 1.5T functional magnetic resonance imaging data were collected from 11 participants, showing that the left posterior inferior temporal region, which has previously been termed the Language Formulation Area (LFA), responded to cloze probability. It is suggested, based on anatomical positioning and a literature review, that the responsiveness of the LFA to cloze probabilities may reflect a role in coordinating the lexical and non-lexical reading pathways. Finally, it is noted that previous studies have implicated this region in dyslexia and some speculations are made in this regard.

PET/CT and SPECT/CT dosimetry in children: the challenge to the pediatric imager.

Both positron emission tomography (PET) and computed tomography (CT) contribute significantly to the effective dose from PET/CT imaging. For PET imaging, the effective dose is related to the administered activity and age of patient. For CT, there are many factors that determine effective dose. Effective dose is dependent on tube current (mA), tube potential (kVp), rotation speed, pitch, slice thickness, patient mass, and the exact volume of the patient that is being imaged. The CT scan may be acquired at exposure parameters similar to those used for diagnostic CT, but more commonly, the tube current is reduced and a localization CT scan of somewhat less than optimal diagnostic quality is obtained. A very low dose CT scan for attenuation correction may also be considered.

Anatomical asymmetries of anterior perisylvian speech-language regions.

Anterior cortical perisylvian areas important for speech and language functions include the pars triangularis (PTR), comprised of heteromodal association cortex, and the pars opercularis (POP), comprised of motor association cortex. The anatomy of these frontal language regions has not been well studied in large samples, however in smaller samples, leftward asymmetry of these regions has been found. Sex-linked differences have also been suggested, with bilateral activation of frontal language areas in women and leftward activation in men. We used volumetric MRI methods to measure the gray matter volume of the PTR, POP, and diagonal sulcus (DS) in 60 healthy right-handed adults and examined the distribution of asymmetry of these regions. Sex-linked differences in volume and asymmetry of anterior speech regions were also examined. For the PTR, there was a slight leftward asymmetry, however for the POP+DS, there was a slight rightward asymmetry. The DS was present slightly more often in the right hemisphere than in the left hemisphere and its frequency was similar in men and women. There were no significant sex-linked differences in volume or asymmetry for any of these frontal areas. More studies are necessary, looking at the anatomy of anterior language regions in large samples and examining the relationship between anatomy and function.

Lobar asymmetries in subtypes of dyslexic and control subjects.

Reading involves phonologic decoding, in which readers "sound out" a word; orthographic decoding, in which readers recognize a word visually, as in "sight reading"; and comprehension. Because reading can involve multiple processes, dyslexia might be a heterogeneous disorder. This study investigated behavior and gross lobar anatomy in subtypes of dyslexic and control subjects. Subjects aged 18 to 25 years with identified reading problems and a group of healthy controls were given cognitive and behavioral tests and volumetric brain magnetic resonance imaging (MRI). Because atypical cerebral laterality has been proposed as a potential neural risk for dyslexia, dyslexic and control subjects were compared on anatomy of gross lobar regions. On asymmetry quotients, no significant differences were found between groups. Examination of the percentage of total brain volume of each structure revealed that control and dyslexic subjects were significantly different (P = .018). Dyslexic subjects had a larger percentage of brain volume than did the controls in the areas of total prefrontal (P = .003; 9.30% larger) and superior prefrontal (P = .004; 11.48% larger region). A Pearson correlation was performed to investigate whether a relationship existed between behavioral measures and either volumes of total prefrontal and total occipital regions or asymmetry quotients. A significant positive relationship between the left total occipital and word identification performance existed (R = .452, P = .045). Because it is believed by some that dyslexia occurs in varying degrees of severity, and because one of the research questions in this study is whether anatomy relates to severity or to distinct biologic groups, subjects were grouped according to both the nature and distinct pattern of reading or language performance and the degree of deficit. A battery of reading tests revealed five clinical subgroups of control (two) and dyslexic (three) subjects. These subgroups were statistically different on all cognitive and behavioral measures. When asymmetry was investigated across subgroups, significant differences between subgroups were found at the multivariate level (P = .043). Only the phonologic deficit groups (weak phonologic controls, phonologic deficit dyslexic subjects) had atypical asymmetry patterns. This finding suggests that lack of subtyping could have confounded earlier studies and that anomalous asymmetry might be related to phonologic dyslexia, whereas other subtypes might be reflective of environmental factors. Examination of volume at the subgroup level also showed differences between subgroups that might have implications for the nature of compensation. This study supports the concept that anomalous anatomy might reflect anomalous functional cerebral laterality, which could be a risk factor for developmental dyslexia, varying according to the nature of the deficit.

Variability in perisylvian brain anatomy in healthy adults.

Gray matter volumes of Heschl's gyrus (HG), planum temporale (PT), pars triangularis (PTR), and pars opercularis were measured on MRI in 48 healthy right-handers. There was the expected leftward PT asymmetry in 70.8%, and leftward PTR asymmetry in 64.6% of the sample. When asymmetry patterns within individuals were examined, there was not one typical pattern, rather several typical configurations were found. In addition, some combinations of asymmetry did not exist in our sample suggesting that some perisylvian anatomical configurations may provide a more suitable neural substrate for the development of language than others. There were also sex differences in HG. Men had rightward asymmetry and women demonstrated leftward asymmetry, due to women having smaller right HG, compared to men.

Sex-linked differences in the anatomy of the perisylvian language cortex: a volumetric MRI study of gray matter volumes.

Perisylvian regions important for auditory processing include Heschl's gyrus (HG), the planum temporale (PT), the posterior superior temporal gyrus (pSTG), and the posterior ascending ramus (PAR). Sex-linked differences in language functions and anatomy have been suggested. To examine sex-linked differences, the authors used MRI to measure HG, PT, pSTG, and PAR volumes. Sex differences were found in right HG and right pSTG volumes but not in the left volumes of these structures. For the PT, there were sex differences in asymmetry; women exhibited leftward asymmetry of the PT, whereas men did not exhibit PT asymmetry. These findings suggest that there are sex-linked differences in the anatomy of primary and association auditory cortices.